1. Technical Field
The present application relates to a voltage converter and a power supply system including the voltage converter. In particular, the present application relates to technology for converting the voltage of direct-current voltage supplied from a battery and using the converted voltage to drive an electric vehicle.
2. Description of the Related Art
As a power supply device for electric vehicles, a power supply device is widely used that increases the voltage of a direct-current power supply, such as a battery, using a boost circuit and supplies a high voltage that is higher than the battery voltage to a drive section of an electric vehicle. The boost circuit has a reactor, a capacitor, a switching element, and a diode. For example, in a power supply device disclosed in JP-A-2010-268626, a boost circuit has a reactor and a capacitor and, therefore, has a resonant frequency. On the other hand, with the increased voltage as the direct-current power supply voltage of an inverter, the drive section of an electric vehicle converts the direct current to a three-phase alternating current in the inverter and supplies power to an alternating-current motor. The alternating-current motor is known to cause periodic voltage fluctuations in the direct-current power supply voltage of the inverter. The voltage fluctuations are attributed to, for example, detection errors in measurement devices (current sensors and rotation angle sensors). When the periodic voltage fluctuations in the drive section match the resonant frequency of the boost circuit, excessive voltage may be applied to the switching element in the boost circuit. The switching element may be destroyed. JP-A-2010-268626 discloses a method in which destruction of the switching element is prevented by reducing a boost voltage command value when the frequency of the voltage fluctuation in the drive section approaches the resonant frequency of the boost circuit.
However, in the conventional technology, the inverter power supply voltage is reduced when the frequency of the voltage fluctuation in the drive section approaches the resonant frequency of the boost circuit. Therefore, an issue arises in that, although limited, reduced vehicle driving force is unavoidable.